1. Field of the Invention
The present invention relates to an image forming apparatus that corrects positional deviations of images formed by a plurality of image forming units.
2. Description of the Related Art
Currently, an electrophotographic image forming apparatus that forms multicolor images forms the multicolor images by superimposing images in a plurality of colors, and therefore needs to correct positional deviations between the images in the plurality of colors, that is, needs to correct color misregistration. A method is known in which color misregistration amount detection patterns are formed on an intermediate transfer belt and the amount of color misregistration is detected by reading the color misregistration amount detection patterns using an optical sensor, and then the color misregistration is corrected by correcting the image forming timing for each color (Japanese Patent Laid-Open No. 2003-098795). If the speed of the intermediate transfer belt or the like has changed due to a disturbance while the color misregistration amount detection patterns are being formed or read and an amount of color misregistration larger than the actual amount has been incorrectly detected, incorrect color misregistration correction is undesirably performed. In order to prevent the incorrect color misregistration correction, a method has been proposed in which, if an amount of color misregistration larger than a certain amount has been detected, color misregistration correction based on this amount is not performed.
However, in the case of the configuration with which an amount of color misregistration larger than the certain amount is always ignored, color misregistration correction cannot be performed even when color misregistration whose amount actually exceeds the certain amount is caused. For example, when the position of a unit in the image forming apparatus has changed due to replacement of the unit, a large amount of color misregistration can be caused.